Time to regain birth weight predicts neonatal growth velocity: A single-center experience

Failure to Thrive (FTT) describes the development of an inappropriate pattern of growth, generally secondary to inadequate nutritional intake, and is associated with several negative outcomes. We describe key features among neonates with FTT as well as the variables that predicted their growth after birth at a Neonatal Intensive Care Unit.

A retrospective single center study of 340 patients grouped into FTT (n = 100) and non-FTT (n = 240) was conducted. FTT was defined as having a weight <10th percentile on the Fenton 2013 curve at the time of discharge. For analyzing growth velocity, 204 patients were grouped into 4 quartiles based on their calculated growth velocity (grams/kilograms/day [g/kg/day]; 4th quartile had the highest velocity). Multivariate regression models were used to identify predictors of growth velocity.

When comparing FTT vs. non-FTT patients, lower birth weights (1897.9 ± 561.4 vs. 2445.9 ± 783.0 g, t_(255.1) = -7.2, p < 0.001) and higher growth velocities (9.2 ± 3.9 vs. 8.0 ± 4.1 g/kg/day, t_(153.6) = 2.2, p = 0.03) were noted. Among patients with higher growth velocities, birth weights were lower (1st to 4th quartiles: 2474.0 ± 677.0, 2000.0 ± 297.0, 1715.0 ± 285.0, 1533.0 ± 332.0 g, F_{(3, 200)} = 46.5, p < 0.001, adjusted R² = 0.4). Days to regain birth weight was the most consistent predictor of growth velocity in our overall patient sample (β [SE] = -0.3 [0.03], p < 0.001) and in the lowest growth velocity quartile subgroup (β [SE] = -0.3 [0.04], p < 0.001).

Days to regain birth weight was consistently the strongest predictor of neonatal growth velocity along with difference in gender positive predicting growth velocity in the total sample. This highlights the importance of the first week of life in growth pattern establishment.